Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 40, § 5C

To provide for extraordinary or unforeseen expenditures, a district may at an annual or special district meeting appropriate or transfer a sum or sums not exceeding, in the aggregate, five per cent of the receipts from taxes, rates and services of the fiscal year preceding the fiscal year for which the fund, to be known as the reserve fund, is established. No direct drafts against this fund shall be made, but transfers from the fund may from time to time be voted by the prudential committee, if any, otherwise the commissioners; and the district treasurer shall make such transfers accordingly.